Web tensioning device with improved excursion control

ABSTRACT

A web tensioning device utilizes a dancer device, either angular or linear, which can be positioned by a controlled servo motor. In a preferred embodiment, the controller for the servo motor receives an input signal based on the acceleration (positive or negative) of the dancer device caused by a web excursion and implements a compensation necessary to oppose the web excursion. The controller may also receive additional input signals indicative of the acceleration of the web itself, resulting from the web excursion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 10/717,019 filed Nov. 19, 2003, now U.S. Pat. No. 7,438,251, which, in turn, is a continuation-in-part of U.S. patent application Ser. No. 10/465,219 filed Jun. 19, 2003, now abandoned, the disclosures of which are fully incorporated herein.

FIELD OF INVENTION

This invention relates to devices for tensioning webs, such as paper webs or textile webs, during processing. More particularly, this invention relates to ongoing dynamic control of excursions of web tension

BACKGROUND OF THE INVENTION

Web tension control is important in paper conversion processes and the like. In high speed operations, even relatively small web excursions such as variations in web tension may cause web processing difficulties downstream. Moreover, in relatively high speed web lines, such as those exceeding about 500 feet per minute (about 150 meters per minute), manual adjustment of web tension is not practical.

In web tensioning systems where web tension is controlled or maintained by a dancer, a limitation on effective control of web tension is the response time of the dancer inasmuch as often the dancer movement lags behind the actual changes in web tension. A primary cause of such relatively long response time is the weight of the dancer. Thus, it would be desirable to have a web tensioning device that responds readily to variations in web tension with minimum lag time. The present invention satisfies this need.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a novel and an improved web tensioning device that minimizes the disadvantages associated with the prior art devices and provides advantages in construction, mode of operation and use.

In other aspects, the present invention achieves numerous benefits by overcoming a web excursion that causes a dancer device (e.g. rotatable dancer arm or linear dancer roller) in contact with the web to accelerate under an excursion force. The present invention, in certain aspects, operates by applying to the dancer device an opposing compensating force component, either angular or linear. The compensating force component, exclusive of any adjustments to the compensating force for components of the web tensioning device being employed, is substantially the same in magnitude as the excursion force.

In one example, the present invention overcomes a web excursion that causes a dancer device (e.g. rotatable dancer arm or linear dancer roller) to undergo an excursion acceleration arising from an excursion force imparted to the dancer device by the web excursion. This compensation of the effects of a web excursion is achieved by providing a controller for generating a control output signal for a servo motor that is operably associated with the dancer device. The control output signal causes the servo motor to apply an opposing compensating force component to the dancer device in response to the excursion acceleration as detected by a dancer device acceleration or position sensor, a web sensor, and the like. The magnitude of the opposing compensating force is substantially the same as the magnitude of the excursion force imparted to the dancer device.

The present web tensioning device includes a base, a dancer device, preferably with at least one dancer movably mounted to the base, and a servo motor that applies a force to the dancer device in response to a control output signal which depends on web tension requirement at a given point in time. The control output signal to the servo motor is provided by a controller that is operably associated with the servo motor and is responsive to a web tension requirement communicated to the controller either by displacement of the dancer arm or a web feed rate actuator. The dancer device can be provided with plural dancers, e.g., two or four dancers, if desired. Moreover, a particular web conversion machine can utilize more than one dancer arm. The dancer can be a dancer roller, a fixed shaft, an air bearing fixed shaft, and the like. The dancer device can be pivoting as well as a straight running accumulator, as desired.

In one particular embodiment, the present web tensioning device includes a dancer arm suitable for engaging the web to be tensioned. The dancer arm has a free end portion that carries a dancer roller mounted thereon and a fixed end portion that is pivotably mounted to a base and so as to coact with an angular position sensor that indicates the relative angular displacement of the dancer arm while tension is maintained in the web. The web can be a paper web fed to a paper converting machine, a fabric web, and the like.

A servo motor is operably associated with the dancer arm for pivotally positioning the dancer arm in engagement with the web by application of a torque in response to a control signal from a controller. Input to the controller can be provided by the angular position sensor, a position feedback device such as an encoder, and the like, that monitors the angular displacement of the dancer arm from a predetermined position as the web is fed from an unwind roll to further processing station or stations.

In another particular embodiment, the present web tensioning device includes a dancer roller suitable for engaging the web to be tensioned. A dancer roller is mounted to a linear motor and preferably includes a rotational mounting to accommodate the speed of the traveling web in contact with the dancer roller. The linear motor is in turn, mounted to a base so as to coact with the dancer roller to respond to excursions of the traveling web in contact with the dancer roller. A linear sensor is provided to detect displacement of the dancer roller as it responds to a web excursion. The web can be a paper web fed to a paper converting machine, a fabric web and the like.

A controller is coupled to the linear sensor to adapt the sensor output to a responsive compensating force signal. The compensating force signal is applied to a linear motor operably associated with the dancer roller so as to oppose displacement of the dancer roller caused by the web excursion. The magnitude of the opposing compensating force is substantially the same as the magnitude of the excursion force imparted to the dancer device that arises from the web excursion.

BRIEF DESCRIPTION OF THE DRAWING

In the drawings,

FIG. 1 is a schematic depiction of the web tensioning device according to aspects of the present invention and utilizing a position feedback mode of operation;

FIG. 2 is a schematic depiction of web tensioning dancer arrangement that utilizes a pair of dancers mounted to a dancer arm;

FIG. 3 is a schematic depiction of web tensioning dancer arrangement that utilizes four dancers mounted to a dancer arm;

FIG. 4 is an exploded perspective schematic depiction of a web tension device according to certain aspects of the present invention;

FIG. 5 is a schematic diagram of another web tensioning device embodying the present invention;

FIG. 6 is a schematic diagram of a slider controller;

FIG. 7 is a perspective schematic depiction of yet another web tensioning device embodying the present invention;

FIG. 8 is an exploded perspective depiction of a further web tensioning device embodying the present invention; and

FIGS. 9-13 are schematic diagrams of additional web tensioning devices according to various aspects of the present invention.

In the FIGURES, legends having the same last two digits denote elements that perform the same or similar function.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention disclosed herein is, of course, susceptible of embodiment in many different forms. Shown in the drawings and described herein below in detail are preferred embodiments of the invention. It is understood, however, that the present disclosure is an exemplification of the principles of the invention and does not limit the invention to the illustrated embodiments.

For ease of description, web tensioning equipment utilizing features embodying the present invention are described herein below in their usual assembled position as shown in the accompanying drawings, and terms such as upper, lower, horizontal, longitudinal, etc., may be used herein with reference to this usual position. However, the web tensioning equipment may be manufactured, transported, sold, or used in orientations other than and described and shown herein. An industrial web converting machine usually performs its processing functions utilizing a continuous sheet or web of paper or other non-woven material (e.g., yarn, wire, tubing, or filament), fabric, foil, and the like. The web can be pulled by one or more power driven rollers through a series of idler (or non-driven) rollers to one or more processing stations or stages where the web is folded, cut into segments, shaped, etc. The web is fed into the machine from a relatively large roll called an “unwind roll” which rotates on a roll stand.

The web may travel at different speeds through different sections of the converting machine and becomes slack from time to time, either by design or otherwise. A web that is slack can become undesirably tangled or wrinkled. To control slack, a web processing system frequently utilizes a dancer which typically is one or more idler rollers or shafts on non-rotating arms that move freely against the web, usually by being mounted on a pivoting arm of some sort. The dancer controls web tension by increasing or decreasing at any point in time the accumulation (festoon) of the web at a given location. Under balanced or steady state conditions the dancer remains stationary, i.e., in a neutral position, but is positioned as needed depending on whether web tension, especially local web tension is to be increased or decreased as a result of the operation of the web converting machine or the like.

In a typical application, a dancer is mounted to a pivotably mounted arm to which a positioning force is applied by a spring, a solenoid, a pneumatic cylinder, a hydraulic cylinder, and the like force generator. The positioning force urges the dancer tightly against the web.

In one kind of web excursion, a condition is encountered, where an out-of-round unwind roll or variable tension produced by an unwind mechanism, that causes cyclical web acceleration followed by web deceleration at a relatively high frequency. As a result, the dancer rapidly moves back and forth due to a force supplied by the web to move the mass of the dancer as the web tension cycles between tight and loose. Such rapidly alternating web tension necessarily leads to operating problems downstream, and thus a need for a controlled loop or festoon to provide time for correcting web excursion condition on the converter.

The present invention obviates such problems by simulating a “zero mass” dancer vis-a-vis the web in contact therewith. To that end, a driven, active element such as a servo motor is utilized in lieu of the conventional force generators that have been used to pivot the dancer arm and tension the web. Any action by a web excursion that causes the dancer arm to shift position is monitored by a position sensor, typically an encoder, such as a rotary encoder, although an accelerometer or virtually any type of position displacement sensor known today, whether angular or linear, can be utilized as well. An output signal from the position sensor is transmitted as input to a controller that signals the servo motor to compensate (e.g. correct or otherwise react to) the web tension so as to return the dancer arm to its predetermined steady state or “neutral” position.

The term “servo motor,” as used herein and in the appended claims, means an electric, hydraulic or other type of motor, including a limited angle motor, rotary motor, linear motor, embedded motor, solenoid, pneumatic actuator and the like, that serves as the control element of an automatic feedback control system for mechanical motion. A preferred motor is a torque feedback electric motor.

The term “motion control element” as used herein and in the appended claims, means an apparatus for applying a compensating (e.g. corrective or otherwise reactive) force to a system component for which control is provided according to aspects of the present invention. In one example, the system component contacts the web so as to affect its tension. Motion control elements, as contemplated herein, can be of either angular or linear type, imparting either angular or linear forces to the subject system component. Some form of control, e.g. feedback or feed forward control is usually applied to the motion control element to impart the desired compensation to the subject system component.

The term “linear motor,” as used herein and in the appended claims, means a motion control element imparting one or more linear forces to the subject system component for which compensating (e.g. correcting or other reacting) control is provided according to aspects of the present invention. Linear motors contemplated by the present invention can take different forms, although a linear induction motor is preferred.

The term “accelerometer” as used herein and in the appended claims, means virtually any type of device with or without associated circuitry for sensing acceleration, usually the acceleration of the system component for which control is provided according to aspects of the present invention. Typically, when provided, an accelerometer is used to provide feedback or feed forward control for the motion control element(s) employed to impart a correction or other compensation to a system component, as may be desired.

The present invention provides improved control of local web excursion events, e.g. excursions in tension, of a local portion of a traveling web, such as a web portion in contact with a dancer device, either angular or linear. The excursions in web tension are applied to the dancer device, causing the position of the dancer device to undergo a displacement from a steady state position (i.e. a position of the dancer device immediately prior to the excursion event). The dancer device is displaced with an acceleration of observed magnitude, and according to aspects of the present invention, a compensating force of similar magnitude, is applied in an opposing direction to the dancer device to resist its displacement, thereby overcoming the web excursion.

Referring to FIG. 1, a web tensioning system 10 is shown utilizing web tensioning device 12 engaging a tensioned segment of traveling web 14 which also contacts idler roll 40. Web tensioning device 12 includes dancer arm 16 that carries at the free end 18 thereof a dancer, such as rotatably mounted dancer roll 20 that also serves as a web redirect roller. As shown in FIG. 1, the tensioned segments 14 appearing at the left and the right sides are vertically offset, one from the other, but are preferably maintained generally parallel to one another. If desired, these tensioned segments 14 can also be angularly offset from one another, although this may require slightly different control settings.

Fixed end 22 of dancer arm 16 is pivotably mounted to base 24 by shaft 26 which is affixed to dancer arm 16 and in turn is journaled in base 24.

Also fixedly mounted to shaft 26 is an encoder, such as incremental rotary optical encoder 30, which serves as an angular position sensor and indicates the relative angular position of pivot shaft 26, and thus dancer arm 16. Information from the rotary optical encoder 30 provides an appropriate input signal to dancer control 34. The encoder can be an incremental encoder or an absolute encoder, as desired.

Operably mounted to pivot shaft 26 is an angular motion control element in the form of a limited angle electric servo motor 36 which turns pivot shaft 26, and thus positions dancer arm 16 by pivoting it in response to a control output signal from dancer arm controller 34. The output signal is applied via an output line coupling dancer arm controller 34 to servo motor 36, as shown in FIG. 1. In this manner, initial steady state tension on the web 14 can be set to a predetermined value and thereafter maintained. During a web excursion event, a relatively small rotation displacement of pivot shaft results from a change in web tension. This displacement provides information via encoder 30 that serves as input signal to controller 34. Preferably, controller 34 includes a signal processor for processing the sensor output signal and, if necessary, a servo amplifier to scale and/or convert the signal processor output so as to be usable by the particular servo motor employed in the web tension device. For example, a servo amplifier may be employed to scale and/or convert the signal processor output to a form and magnitude range that is usable for the particular servo motor employed.

Preferably, the sensor signal is processed rapidly (preferably as instantaneous as is practical) by dancer controller 34, so as to send a controller output signal to energize servo motor 36 via the output line shown in FIG. 1. The controller output signal determines the magnitude and direction of the servo motor's torque output necessary to maintain the desired tension in the web. Included in the controller output signal applied to the servo motor are any adjustments needed to obtain the desired motion of the dancer arm needed to attain a desired operational result. According to one aspect of the present invention, the desired operational result may be to return the web to its steady state condition (e.g. web tension) that occurred immediately prior to the web excursion that triggered the web control device to take compensating (e.g. correcting or other reacting) action. The controller output signal may, for example, include an initial increased bias force (increased beyond that necessary to maintain a steady state tension goal) that is necessary to overcome inertia of the web control device, so as to attain the desired operational goal of the web as quickly as is practically possible. As another example, the response of the dancer arm preferably conforms to a desired acceleration curve, chosen to match the acceleration curve of the control arm excursion. Other control techniques may be provided by the controller, as well, as is known in the art.

Preferably, the amount of torque to be provided by the web control device is substantially the same as the dancer acceleration or deceleration force (i.e., positive or negative acceleration force) experienced during ongoing system operation, whatever the case may be. The response time of the servo motor 36 to the control output signal provided by dancer control 34 is relatively short (preferably, as practically immediate as is possible), usually on the order of about one-half millisecond (0.0005 seconds) or less. Thus the torque supplied by servo motor 36 balances out the dancer excursion forces as they occur, and, with beneficial operation of the present invention, web tension remains substantially constant so that the dancer has substantially no inertia to overcome. With respect to the web dynamics, the dancer operated with benefit of the present invention appears to have “zero mass.”

The aforedescribed operation of web tensioning system 10 usually is carried out according to so-called feedback control techniques. A compensating torque or other command component is supplied close in time, and most preferably practically immediately, to servo motor 36, so as to result in a compensation (preferably, a correction or other reaction) in proportion to measured acceleration or deceleration of the dancer caused by the excursion. In any given application, accuracy of the feedback control techniques employed is affected by the inertia of the moving parts of the web tensioning device, accuracy of the acceleration and deceleration measurement of the excursion, and the information processing rate of the controller. As is known in the art, dancer control 34 can be programmed to provide operational adjustments (static or dynamic) to provide compensation, correction or other reaction for inaccuracies or other shortcomings arising from the particular system components employed. If necessary, so-called predictive or “feed forward” control can be added to supplement the aforementioned feedback control, using system modeling techniques, as is known in the art.

Other control arrangements can also be employed by the web control system. For example, a control method can be utilized for web tensioning that also includes a control input signal based on web feed rate or web acceleration at any desired stage of web processing downstream or upstream of the dancer arm. Additional control input to dancer control 34 can be provided via line 38, for example, by a web feed rate actuator in an additional control loop that includes servo motor 36 and dancer control 34. Dancer control 34 could then be modified to serve as combined feedback and feed forward controller to provide a total systems control for web tensioning. That is, a compensating torque (or other) command component can (ignoring adjustments necessitated by system shortcomings or compromises) be applied in proportion to web acceleration or deceleration information obtained from the web feed rate actuator or the like. For this purpose feedback as well as feed forward control strategies can be utilized to sense and/or predict deviations from a set point and to provide compensation therefor before and/or immediately after a controlled variable such as web tension materially deviates from the set point.

Inertia effects on the web that is being processed can be further minimized, if desired, by the use of plural dancers carried on the same dancer arm. FIG. 2 illustrates an embodiment having a pair, i.e., two, dancers 120 and 121 rotatably mounted to straight running dancer arm 116 and engaging web 114 with the assistance of idler rollers 140, 141 and 142. As a further alternative, overall systems control responding to one or more inputs, can be split among two or more dancers that apply their respective compensations (e.g. corrections or other reactions) to one or more local portion of the web.

FIG. 3 illustrates yet another embodiment having an array of four dancers 220, 221, 223 and 225 rotatably mounted to dancer arm 216 and engaging web 214 with the assistance of idler rollers 240, 241, 242, 243 and 244. The differences in web tension that are achievable by varying the number of dancers on the same dancer arm are illustrated by the calculations below.

Assuming a web acceleration from Point A to Point B of 1 meter/second² (m/s²) and a dancer mass of 1 kilogram (kg), the theoretical acceleration (i.e., neglecting friction and rotational inertia) of the single dancer shown in FIG. 1 is 1 m/s²÷2 or 0.5 m/s². Thus the force on the web generated by dancer acceleration, force=(mass)(acceleration), is 1 kg×0.5 m/s² or 0.5 Newtons (N), and the tension on the web is 0.5 N÷2 or 0.25 N.

Applying the same assumptions to the dancer system shown in FIG. 2, the theoretical acceleration of each dancer is 1 m/s²÷4 or 0.25 m/s² and the total force on the web generated by dancer acceleration is 2 kg×0.25 m/s² or 0.5 N. However, the tension on the web in this case is distributed over four web portions and is calculated to be 0.5 N÷4 or 0.125 N.

When the same assumptions are applied to the four dancer-system shown in FIG. 3, the theoretical acceleration of each dancer is even less, i.e., 1 m/s²÷8 or 0.125 m/s². The total force generated by dancer acceleration is 4 kg×0.125 m/s² or 0.5 N, but the tension on the web is distributed over eight web portions and is reduced to 0.5 N÷8 or 0.0625 N.

In addition to the sensors described above, the present invention also contemplates use of a torque sensor described in a paper entitled “Torque Sensor Based on Tunnel-Diode Oscillator”, published by NASA's Jet Propulsion Laboratory, NASA Tech Brief reference NPO-43325, Jul. 1, 2006. Included is a concentric arrangement of a solid inner drive shaft disposed within a hollow outer drive shaft. The inner and outer drive shafts are joined together by three flexural springs that couple torque between the inner and the outer shafts. The torque is deduced from the torsional relative deflection of the two shafts, which is sensed via changes in capacitances of two capacitors defined by two electrodes attached to the inner shaft and a common middle electrode attached to the outer shaft. Each capacitor is part of a tunnel-diode oscillator circuit, and each is coupled to the rest of its oscillator circuit via a rotary transformer, to eliminate need for wire connections between the shaft and the stationary part of the machine being monitored.

Linear Control Elements and Systems

In addition to angular control techniques, such as those employing angular motion control elements, as described above, the present invention also contemplates linear control techniques, e.g. techniques employing linear motion control elements, such as, a “linear motor,” defined herein as a linear motion control element having a fixed stator supporting a moveable translator or slider. By comparison to angular motion control elements, the translator or slider is roughly equivalent to a rotor in an angular system. Preferably, the stator and slider are unconnected to each other (other than the sliding relationship of the slider with respect to the stator. In the preferred embodiment, the linear motor preferably takes the form of a linear induction motor.

The stator includes one or more components of the motor, such as windings and slide bearings intended to support the slider of the linear motor device and not the loads applied thereto, such as loads imparted by a dancer roll. The stator may also include accelerometers and/or other types of sensors, e.g. those providing position or velocity detection and temperature monitoring. Components of the stator are integrated into a physically robust metal stator housing of rectangular, circular or other cross-sectional shape. Preferably, the stator housing defines the path of travel of the slider.

The slider contains magnets and fittings for connection to the device to be controlled, such as a dancer roll or other component of the overall web transport system. The slider includes a physically robust outer housing, which is adapted for reciprocal sliding along the stator housing. Preferably, there are no electronic connections between stator and slider, although a connection between the slider and external control circuitry is preferably provided. For example, accelerometers or other external electronic sensors may be carried on the outside of the slider housing, with related electrical connections fed through the slider housing and connected to the electronics within the slider housing. If desired, all sensors, control circuitry and other electronics may be carried within the slider housing. Acceleration and/or other sensing and detection may be done on a contact-free basis using wireless coupling, using, for example, magnetic field sensors in the stator.

In operation, loads applied to the system being monitored, e.g. a dancer roll, are coupled to sensors associated with the slider Upon sensing a web excursion, control circuitry associated with the slider sends commands to the slider to apply a compensating force that responds to a change of the dancer roll away from a predefined “normal” or “steady state” condition. One example of a normal or steady state condition is that experienced by the dancer roll with the web operating at the desired tension. The compensating force preferably opposes the change to which the dancer roll is subjected, so as to return the dancer roll to its “normal” condition, in a practically immediate fashion, preferably on the order of tenths or even hundredths of a milliseconds or so.

Referring now to FIG. 4, a web tension device generally indicated at 300 utilizes a linear control element in the form of a linear motor 302 carried on a mounting plate 304. An elongated traveling web 306 of flexible material enters device 300 at inlet roller 308 and exits the device at outlet roller 310. An intermediate dancer roller 312, located between inlet and outlet rollers 308, 310 is movably mounted with respect to mounting plate 304 and an opposing plate 314, whereas the inlet and outlet rollers are not. As shown, the rollers 308-312 have shafts at their opposed ends, for rotational mounting to plates 304, 314. The shafts of inlet and outlet rollers 308, 310 are mounted in journals 318 provided in plates 304, 314 whereas the shafts of dancer roller 312 are mounted at one end in journal 322 of slider 324, and at the other end to journal 326 carried by a sliding carriage 328 that is slidably mounted in plate 314.

As is appreciated by those skilled in the art, as web 306 travels along the web processing system, the web experiences excursions away from a so-called steady state operation, such as a state of constant predefined velocity. Such excursions may take the form of accelerations (positive or negative) that appear locally, at the site of tension control device 300.

Slider 324 forms a movable part of a linear control element that preferably takes the form of a linear motor 330. A stator 332 in the form of a bar having a rectangular cross-section also forms a stationary or fixed part of linear motor 330. Stator 332 includes an outer housing 336, whereas slider 324 includes an outer housing 338. Preferably, the stator and slider are unconnected to each other (other than the sliding relationship of the slider with respect to the stator). Slide bearings on one or both of the stator and slider components enable the stator to support the slider and preferably, the slider alone, exclusive of loads coupled to the stator through the slider, and arising from loads imparted to the dancer roll 312 by moving web 306.

Stator 332 of the preferred embodiment includes windings for linear induction motor operation, cooperating with magnets carried by slider 324. Stator 332 may also include other internal components such as accelerometers and/or other types of sensors, e.g. those providing position or velocity detection as well as temperature monitoring. Components of the stator are integrated into a physically robust metal stator housing 336 that may have a rectangular, circular or other cross-sectional shape. Preferably, the stator housing defines the path of travel of the slider. Alternatively, as is preferred in the illustrated embodiments described herein, sensors used to provide control for the slider are external to both the slider and the stator.

Fittings carried by the slider, e.g. the journal 322, provide mounting for the controlled object, herein the dancer roll 312, so as to be carried for movement along the path of travel defined by the stator 332. Preferably, journal 322 also provides rotational mounting (preferably uncontrolled) for the dancer roll, allowing the dancer roll to provide frictionless support for the traveling web 306. The opposed end of dancer roll is supported by journal 326, carried by carriage 328, which in turn is mounted for reciprocal linear movement along guide bars 342 that are fixedly mounted to plate 314.

As will be seen herein, linear motor 330 can be used with a variety of controllers that govern operation of slider 324, especially to apply a compensating (e.g. corrective or other reactive) force to the slider to overcome a recent or anticipated excursion of the dancer roller 312 caused by forces imparted to the roller by the traveling web 306. Generally, some form of sensor signal is acquired and routed to the controller, and the controller, in turn sends a controller signal to the slider 324 of the linear motor 330 to provide the desired compensation, correction or other reaction to quickly restore the dancer roll and hence the web tension to its predefined steady state condition. Preferably, the controller employs feedback or feed forward techniques, or both, to provide very rapid, as instantaneously as is practical to do so, the desired compensation, correction or other reaction.

Referring now to FIG. 5, a web tensioning device generally indicated at 350 includes a linear motor 330 mounted to a frame 304. A controller generally indicated at 354 includes a sensor, preferably in the form of an accelerometer 356 carried on slider 324. The accelerometer 356 senses acceleration of slider 324. Of interest here are accelerations of slider 324 in response to external forces coupled to the slider through dancer roller 312 and journal 322, originating with excursions of traveling web 306 from a steady state condition. For example, if tension of web 306 suddenly increases (one example of an excursion from steady state operation), dancer roller 312, journal 322 and hence slider 324 will be biased, i.e. accelerated to the rightward direction of FIG. 5. Controller 354 and linear motor 330 cooperate to compensate, correct or otherwise react to this excursion, to return dancer roller 312 to its steady state condition (preferably the normal operating condition of the web, prior to the excursion).

The output of accelerometer 356 is fed to signal processor/controller 358 that responds to the accelerometer output signal by sending a signal to servo amplifier 360, which preferably operates as the driver for slider 324, converting input signals into the type and range of signal required to physically drive the slider 324 along the stator of linear motor 330, to thereby develop the desired compensation, either during its excursion or immediately thereafter, or both. The present invention contemplates compensations, corrections or other reactions that take place all at once, and/or that takes place over a relatively narrow window of time. As will be appreciated by those skilled in the art, various algorithms and other calculations may be provided to signal processor 358 and/or servo amplifier 360, and a wide variety of techniques are available to cause controller 350 to provide the desired compensation, correction or other reaction to slider 324, embodied as one or more electrical signals sent to slider 324 along line 362. If desired, pneumatic or hydraulic signals may also be applied to the slider and may serve as the basis for operation of one or more components of controller 350.

In operation, accelerometer sensor 356, mounted on the movable slider 324 to which the dancer roller 312 is also mounted, detects changes in dancer position and the output signal from the signal processor 358 responds to calculations of acceleration of the dancer roller that are associated with its position change. The servo motor 330 is given a force signal on line 362, that is based on the amplitude of the dancer acceleration and which operates to accelerate the dancer roller to maintain, for example, a steady force on the web 306.

In the embodiment shown in FIG. 5, only one side of the dancer roller is driven by linear motor 330. As shown in the web tensioning device 370 of FIG. 7, both opposed ends of dancer roller 312 may be operated by respective linear motors 330, constructed and operated as is described above. Because both ends of the dancer roller are now driven with a compensating, corrective or other reactive acceleration, the desired control goal state may be achieved much more quickly, a feature of interest when unusually heavy or stiff webs are being processed. With the use of two linear motors, the web tensioning device 370 may be employed to impart a compensating, corrective or other reactive adjustment to any lateral shifting of web 306 to one side or the other.

With reference to FIG. 6, a generalized schematic diagram of web tension devices according to certain aspects of the present invention is shown. Slider 324 of linear motor 330 is driven by a control unit 500. Included in control unit 500 are three idealized, generalized components that are separately indicated, but which can be combined one with the other, as may be desired. Control unit 500 includes a sensor S, signal processor 358 that processes the output of sensor S, and a servo amplifier 360 that preferably scales or translates the signal processor output so as to be usable by the particular slider device being employed. The sensor S may take a variety of forms, and examples are given herein. Included among the possibilities are accelerometers, doppler lasers, linear encoders, lasers, linear transducers and analog proximity sensors. If desired, multiple sensors can be employed, and their signals processed by a common signal processor, as may be desired. If desired, the signal processor and optional servo amplifier can be combined to form a controller, which in association with the sensor, provides a convenient package for controlling operation according to principles of the present invention, as set forth herein.

The sensor S preferably detects position, velocity or acceleration of either web 306 and/or slider 324 arising from a web excursion. Signal processor 358 processes the sensor output to provide a signal responsive to the movement, most preferably the acceleration, of the object being sensed arising from a web excursion. As contemplated herein, the object being sensed is preferably either the web or the slider, or both, because of their close relationship to web handling performance. Other objects along the web path can also be sensed, if desired.

The arrangement shown in FIG. 7 depicts so-called single lane web processing, where a single web is processed. In many applications it is desirable to process two or more webs simultaneously. FIG. 8 depicts such an arrangement for dual lane, or side-by-side processing of two webs 306. Web control device 380 employs a pair of end walls 314, each having journals 326 for supporting outside ends of dancer rollers 312 as well as infeed and outfeed rollers 308, 310. A middle wall 304 mounts a linear motor 330 that includes a slider 324 having a journal 322 for rotatably supporting the dancer rollers 312 of both web processing lanes. The slider 324 is energized by a controller, not shown, to compensate, correct or otherwise react to excursions of the dancer rollers 312. Because both dancer rollers 312 are supported by the same slider 324, their individual excursions are “averaged” with the same compensation, correction or other reaction being applied simultaneously to the dancer rollers of both lanes. Any of the controllers described herein as well as any controller known in the art may be employed for the purpose.

Referring to FIG. 9, an alternative embodiment of a web tensioning device generally indicated at 390 utilizes a conventional analog proximity sensor 392 that senses the upper surface 394 of slider 324. Preferably, slider 324 includes an outwardly projecting finger 396 to provide a convenient extension of the operating range and hence the resolution of sensor 392, although other arrangements may be employed, as are known in the art. As in other arrangements described herein, the sensor output is fed to signal processor 358, the output of which is fed through servo amplifier 360 to provide drive signals to slider 324.

In operation, the analog proximity sensor 392 detects changes in slider position, and hence dancer position via angled sensing surface geometry. The output signal from the signal processor 358 is responsive to its calculations of acceleration of the dancer roller coupled to slider 324. The slider servo motor is given a force signal based on the amplitude of the dancer acceleration and accelerates the dancer roller (which is coupled to slider 324) to maintain a steady force on the web.

Referring to FIG. 10, web tensioning device 400 includes a linear encoder sensor 402 carried on slider 324. An elongated position index 404 is mounted along the path of travel of the sensor 402, as shown, and communicates with the sensor 402 to indicate the relative position of the slider. The sensor output is fed to signal processor 358 that calculates acceleration of the slider, and feeds a signal responsive to those calculations to servo amplifier 360, to drive slider 324 in the manner of a functioning servo motor, to quickly restore the slider, and hence the dancer roller to its desired steady state position.

In operation, the linear encoder sensor 402 detects changes in slider position, and hence dancer position and the output signal from the signal processor is used to calculate acceleration of the dancer roller. The slider, functioning as a servo motor, is given a force signal from servo amplifier 360 based on the amplitude of the dancer acceleration and accelerates the slider and hence the dancer roller to maintain a steady force on the web.

Referring to FIG. 11, web tensioning device 410 includes a linear transducer sensor 412 carried on slider 324. An elongated position index 414 is mounted along the path of travel of the sensor 412, as shown, and communicates with the sensor 412 to indicate the relative position of the slider 324. The sensor output is fed to signal processor 358 that calculates acceleration of the slider, and feeds a signal responsive to those calculations to servo amplifier 360, to drive slider 324 (which functions as a servo motor), to quickly restore the slider, and hence the dancer roller to its desired steady state position.

In operation, the linear transducer sensor 412 detects changes in dancer position and the output signal from the signal processor 358 is based on calculations of acceleration of the dancer roller. The slider 324 (functioning as a servo motor) is given a force signal from servo amplifier 360 that is based on the amplitude of the dancer acceleration and accelerates the dancer roller to maintain a steady force on the web.

Referring to FIG. 12, a web control device 420 includes a laser sensor 422 that emits a laser beam that is reflected from slider 324, traveling along beam path 424. The sensor 422 emits an output signal responsive to the sensed reflected energy, and its comparison to the emitted beam. The output signal is fed to signal processor 358 that calculates changes in slider position, as well as slider acceleration. Signal processor output is fed to servo amplifier 360, which in turn drives slider 324, treating the slider as a servo motor.

In operation, the laser sensor 422 detects changes in slider position, and hence dancer position sending its sensor signal to signal processor 358. The output signal from the signal processor 358 is based on internal calculations of excursion acceleration of the slider/dancer roller assembly. The slider 324 (functioning as a servo motor) is given a force signal from servo amplifier 360 that is based on the amplitude of the dancer acceleration and accelerates the slider/dancer roller to maintain the steady state condition of the slider.

Referring now to FIG. 13, a web control device 430 includes a laser sensor 432 in the form of a Laser Doppler Velocity sensor or Laser Surface Velocimeter. Laser sensor 432 emits a laser beam that is reflected (along beam path 434), from the incoming web 306. Laser energy is reflected from the web, preferably at a point immediately upstream of infeed roller 308, as shown. The sensor 432 emits an output signal responsive to changes in the sensed velocity of the web. The output signal is fed to signal processor 358 that calculates web excursion acceleration, and optionally, calculates a predicted acceleration of slider 324 (which, by reason of coupling to the web, is responsive to web excursion acceleration). Signal processor output is fed to servo amplifier 360, which in turn drives slider 324, treating the slider as a servo motor.

In operation, the laser sensor 434 senses changes in web velocity, the output signal from the signal processor 358 is based, at least in part, on calculations of excursion acceleration of the slider/dancer roller assembly. The slider (which functions as a servo motor) is given a force or position signal from servo amplifier 360 that is based on the amplitude of the web excursion acceleration/deceleration and positions (preferably, by accelerating the slider/dancer roller) to maintain a steady stable condition of the web using feed forward control techniques. If desired, feedback control may also be employed to control slider 324.

As described above, web tensioning devices include either angular or linear devices and components. However, the same web tensioning device may employ any combination of linear and angular devices and components, as may be desired. For example, angular sensors can provide the basis for drive signals to linear compensating (e.g. correction/reaction) devices, such as linear motors. Of course, data from a linear type of sensor can be readily calculated to appear as if it came from an angular type of sensor, and vice-versa, if desired.

Various applications of web tensioning devices according to aspects of the present invention have been described above. For example, the above description has been directed to web processing systems with single lane linear dancer roller with single linear motor at one end of the dancer roller, web processing systems with a single lane linear dancer roller and with dual linear motors at both ends of the dancer roller as well as web processing systems with dual lane, side-by-side linear dancer rollers with a single common linear motor between the dancer rollers. Virtually any type of web processing system can receive benefit from the various aspects of the present invention as described herein.

Further, web control systems and devices according to the present invention can be implemented using a wide variety of sensor technologies. For example, sensors could be used to measure position, velocity, and acceleration of the web, dancer arm or dancer roller. The inner workings of these sensors could utilize magnetic induction, electromagnetic waves (lasers, radio waves, etc.), sonar (sound waves), or piezoelectric crystals (the piezoelectric effect). Virtually any sensor technology as well as any signal processing technology, known today could be used to implement aspects of the present invention.

As can be seen from the above, the invention herein achieves numerous benefits by overcoming a web excursion that causes a dancer or other device (e.g. rotatable dancer arm or linear dancer roller) or the web itself to accelerate under an excursion force, by applying to the dancer device an opposing compensating force component, either angular or linear, that, (exclusive of any adjustments to the compensating force for components of the web tensioning device being employed,) is substantially the same in magnitude as the excursion force.

More particularly, the invention herein, in one aspect, achieves numerous benefits by overcoming a web excursion that causes a dancer device (e.g. rotatable dancer arm or linear dancer roller) to undergo an excursion acceleration arising from an excursion force imparted to the dancer device by the web excursion, by providing a controller for generating a control output signal for a servo motor coupled to the dancer device, to cause the servo motor to apply an opposing compensating force component to the dancer device in response to the excursion acceleration as detected by a dancer device position sensor or a web sensor, with the magnitude of the opposing compensating force being substantially the same as the magnitude of the excursion force imparted to the dancer device.

The foregoing description and the drawing are illustrative, and are not to be taken as limiting. Still other variations and arrangements of parts within the spirit and scope of the present invention are possible and will readily present themselves to those skilled in the art. 

1. A web tensioning device for overcoming an excursion of a traveling web, comprising: a base; a dancer device for engaging the web, mounted to the base for movement in response to a web excursion; a sensor for detecting a position displacement of the dancer device arising from the web excursion and providing a sensor output signal in response to detected position displacement; a controller coupled to the sensor to receive the sensor output signal and for generating in response thereto, a control signal indicative of a force accelerating the dancer device due to a change in web tension associated with the detected position displacement; and a servo motor coupled to the controller and operably associated with the dancer device to apply, in response to the control output signal, an opposing compensating force to the dancer device that opposes said position displacement of said dancer device, the magnitude of the opposing compensating force being substantially the same as that of the force accelerating.
 2. The web tensioning device according to claim 1 wherein the dancer device comprises a pivotably mounted dancer arm and a dancer roller mounted to the dancer arm.
 3. The web tensioning device according to claim 1 wherein the sensor comprises an angular position sensor.
 4. The web tensioning device according to claim 3 wherein the dancer device comprises a pivotably mounted dancer arm and said servo motor applies to torque to the dancer arm.
 5. The web tensioning device according to claim 1 wherein the sensor comprises a linear position sensor.
 6. The web tensioning device according to claim 3 wherein the dancer device comprises a dancer roller mounted for linear travel and said servo motor applies a linear force to the dancer roller.
 7. A web tensioning device for overcoming an excursion of a traveling web, comprising: a base; a dancer device comprising a dancer roller mounted for linear travel for engaging the web, mounted to the base for movement in response to a web excursion; a linear position sensor for detecting a position displacement of the dancer device arising from the web excursion and providing a sensor output signal in response to the detected position displacement, a controller coupled to receive the sensor output signal and for generating in response thereto, a control output signal indicative of an acceleration of the dancer device due to a change in web tension; and a servo motor coupled to the controller and operably associated with the dancer device to apply, in response to receiving the control output signal, a linear opposing compensating force to the dancer device that opposes said position displacement of said dancer device; the magnitude of the opposing compensating force being substantially the same as that of the force associated with the acceleration of the dancer device, so that the excursion of the web is overcome.
 8. The web tensioning device in accordance with claim 7 wherein the servo motor comprises a linear motor.
 9. The web tensioning device in accordance with claim 7 wherein the linear position sensor includes a laser.
 10. The web tensioning device in accordance with claim 7 wherein the linear position sensor includes a doppler laser.
 11. The web tensioning device in accordance with claim 7 wherein the linear position sensor includes a linear encoder.
 12. The web tensioning device in accordance with claim 7 wherein the linear position sensor includes a linear transducer.
 13. The web tensioning device in accordance with claim 7 wherein the linear position sensor includes an analog proximity sensor.
 14. The web tensioning device in accordance with claim 7 wherein the linear position sensor includes an accelerometer.
 15. A web tensioning device for overcoming an excursion of the traveling web, comprising: a base; a dancer arm pivotably mounted to the base for movement in response to a web excursion; an angular position sensor for detecting an angular position displacement of the dancer arm arising from the web excursion and to provide an output signal in response to the detected position displacement; a controller coupled to receive the sensor output signal and for generating in response thereto, a control output signal indicative of an acceleration of the dancer arm due to a change in web tension arising from the detected position displacement; and a servo motor coupled to the controller and operably associated with the dancer arm to apply, in response to receiving the control output signal, an opposing compensating torque to the dancer device that opposes said position displacement of said dancer device, the magnitude of the opposing compensating torque being substantially the same as that of the force associated with the acceleration of the dancer arm, so that the excursion of the web is overcome.
 16. The web tensioning device according to claim 15 wherein the dancer arm has a free end portion with a dancer rotatably mounted thereon and a fixed end portion pivotably mounted to the base so as to coact with the angular position sensor and indicate relative angular displacement of the dancer arm as a web in contact with the dancer is maintained in tension.
 17. The web tensioning device according to claim 15 wherein the servo motor is operably associated with the dancer arm for pivotally positioning the dancer arm by application of a compensating torque component in response to a control output signal.
 18. The web tensioning device in accordance with claim 15 wherein the angular position sensor is an encoder operably associated with the fixed end portion of the dancer device and senses relative angular displacement of the dancer device.
 19. The web tensioning device in accordance with claim 18 wherein the encoder is an incremental rotary optical encoder.
 20. The web tensioning device in accordance with claim 15 wherein the servo motor is an electric motor.
 21. The web tensioning device in accordance with claim 15 wherein the servo motor is a limited angle electric motor operably associated with the dancer device for pivoting the dancer device by application of torque in response to the control output signal.
 22. The web tensioning device in accordance with claim 15 wherein the angular position sensor is a torque sensor including a tunnel-diode oscillator for detecting torque.
 23. A web tensioning device for overcoming an excursion of a traveling web, comprising: a base; a dancer device for engaging the web, mounted to the base for movement in response to a web excursion; a sensor for detecting a change in the movement of a portion of the web adjacent the dancer device, arising from the web excursion and to provide an output signal in response to the detected movement, a controller coupled to receive the sensor output signal and for generating in response thereto, a control output signal indicative of an acceleration of the dancer device due to a change in web tension arising from the detected movement; and a servo motor coupled to the controller and operably associated with the dancer device to apply, in response to receiving the control output signal, an opposing compensating force to the dancer device that opposes said detected movement of said dancer device, the magnitude of the opposing compensating force being substantially the same as that of the force associated with the acceleration of the dancer device, so that the excursion of the web is overcome.
 24. The web tensioning device in accordance with claim 23 wherein the sensor includes a laser monitoring a portion of the web adjacent the dancer device. 